Electrophoretic mobility (EPM) measurements taken with an automated computer controlled microscope will be used to explore early, clinical diagnostic tests for multiple sclerosis. For such tests cells from the peripheral blood will be used. The instrument allows rapid and very precise measurements of EPM on samples of a size that provide high statistical reliability. Current studies made us realize that EPM measurements of the quality now available can be developed into a highly sensitive and specific analytical method for the study of cell surface receptor sites. Modifications in instrument design and computer software will be made to add the ability for simultaneous measurement of sedimentation velocity and to control remaining instrument sources of variation in electrophoretic mobility.